Pressure sensitive adhesives intended for medical use and in particular for adhesion to the skin of human beings must meet much more complex and varying conditions as compared to adhesives which are intended to be used on well-defined surfaces. This is to be ascribed inter alia to the variability of the surface structure and the surface film of the skin. The variation reflects inter alia age and races but also influence from the local climate is vital for the behaviour of the skin. Furthermore, there may be specific requirements to adhesives to be used for certain applications relating to use by human beings having diseases or handicaps. For instance, adhesives used for carrying ostomy bags or used for treatment of a skin ulcer will be affected not only by the normal variations and differences of the skin but also by the secretions from the stoma or from the wound. Thus, there is a need of an option of a local and individual grading of the adhesive properties of an adhesive to obtain a better and more reliable performance.
Various skin adhesive agents are used today for the above-mentioned purposes.
In existing adhesive agents the surface of the adhesive is consisting of the self-adhesive elastomeric matrix while the hydrocolloids are located embedded beneath in the elastomeric matrix. In order to absorb moisture, the water thus needs to penetrate through the elastomeric matrix before reaching the water absorbing hydrocolloids. This retards the water-absorption and causes that the adhesive agent does not have an immediately adhesion to wet surfaces (wet tack).
It is known to provide adhesive surfaces with discrete areas comprising a further component. Thus, U.S. Pat. No. 4,711,781 to Nick et al. discloses a medicinal self-adhesive plaster which comprises a continuous adhesive coating on one surface of a carrier web, a plurality of non-permeable, separating film elements spaced from each other on the surface of the adhesive coating and a plurality of active ingredient elements containing a medication, each disposed on the surface of one of the separating film elements whereby the medicated active ingredient is isolated from the adhesive composition.
Furthermore, WO 99/38929 discloses an article having a surface showing adhesive properties and a cover layer for protecting the adhesive surface wherein a further component, located in indentations in the surface of the cover layer facing the adhesive surface without being in direct contact with the adhesive surface enables a grading of the adhesive properties of the article.
A very widespread embodiment of skin adhesive agents comprises a self-adhesive elastomeric matrix, in which water-absorbing, swelling particles, the so-called hydrocolloids, are dispersed.
It has been proposed to provide adhesive products having a surface showing adhesive properties and wherein parts of the surface show different properties by incorporating a second component as a part of the surface.
Thus, WO 96/41603 describes an adhesive with graded adhesive properties where the grading is obtained by printing of a non- or less adhering pattern. WO 89/05619 discloses an adhesive, flat skin barrier product comprising a plurality of alternating zones of material of at least two different types, in which at least one type of at least one type of zone consists of a skin-friendly self-adhesive material, the zones of material extending substantially in a parallel manner through the entire thickness of the product in a direction intersecting its flat surfaces.
Furthermore, WO 94/15562 discloses an adhesive, flat skin plate product for use as a semi-manufacture in the production of dressings, skin and wound care devices, fastening means for dressings, ostomy equipment, breast prostheses, wound drains and catheters for incontinence equipment, in particular for men, and for use in electrodes for application to the skin, the said skin plate product having an area being delimited by the periphery of the product, a first surface and a second surface being essentially parallel, and a thickness defined as the distance between the two surfaces measured in a direction being perpendicular to the surfaces, and the said skin plate product consisting of two or more essentially not mixed material units, at least two material units being of different material, of which at least one material unit is a skin friendly self-adhesive material, in which a first material unit extends throughout the area of the entire product, this material unit further constituting at least a portion of the first surface and the second surface respectively, and the additional material unit or units constituting the other portion of the first and the second surface, respectively, and extending at least somewhat into the thickness of the product in a direction which intersects the first or second surface of the product.
Preparation of such adhesive products having a surface showing adhesive properties and wherein parts of the surface show different properties by incorporating a second component as a part of the surface requires rather complicated and partly laborious production measures. Furthermore, the different components often have distinctly different Theological properties, which may cause both processing problems and mechanical stressing of the skin during use of the adhesive product.
Improvements in adhesive properties of pressure sensitive adhesives by irradiation with UV-light or electron beams is known in the art. This kind of radiation has a wavelength below 400 nm, which is sufficient to induce chemical reactions such as polymerisation or crosslinking, i.e. changes in the molecular scale chemical structure. In most cases the radiation is used to activate an essentially non-tacky and non-bonding system to become adhesive.
The use of corona treatment to improve the adhesive properties of pressure sensitive adhesives are also known in the art. The operating mechanism here is molecular scale chemistry such as oxidation or chain scission reactions as well as generation of reactive free radicals and polar active groups at the surface. These reactive and/or polar sites are relatively short-lived, hence obtaining a permanent effect with corona treatment is very difficult.
U.S. Pat. No. 5,702,771 describes a process for improving the adhesiveness of a surface coated substrate by an activating treatment of corona charging or ultraviolet light or combinations thereof.
In general, UV-light or low energy electron beam irradiation and corona treatments only affect the very top surface layers to a depth below 50 nm.
WO 98/54269 discloses adhesive compositions comprising a water-dispersible polyester having very rapid water absorption and thereby improved wet tack. Here, the improved water absorption is obtained by introducing a water dispersible polymer in the self-adhesive elastomeric matrix. This is ascribed to the fact that the water dispersible polymer is present at the surface of the adhesive agent and thus is able to cause an immediately absorption of water.
Electron beam irradiation is an effective procedure to sterilise hydrocolloid containing pressure sensitive adhesives but has a detrimental effect on the water absorption properties of the adhesives.